Various types of medical implant devices have been developed over the years. In many instances, such devices enable humans to live longer, more comfortable lives. Implant devices such as pacemakers, artificial joints, valves, grafts, stents, etc. provide a patient with the opportunity to lead a normal life even in the face of major heart, reconstructive, or other type surgery, for example.
It has been found, however, that the introduction of such implant devices can sometimes lead to complications. For example, the human body may reject the implant device which can ultimately lead to infection or other types of complications. Alternatively, the implant device may malfunction or become inoperative. Therefore, it is desirable to be able to monitor the condition of the implant device. On the other hand, it is highly undesirable to have to perform invasive surgery in order to evaluate the condition of the device.
Still further, it is desirable to be able to monitor conditions related to the use of implant devices. For example, in heart patients it may be helpful to know the extent of occlusion in a stent or graft in order to evaluate the health of the patient. Again, however, it is undesirable to have to perform invasive surgery in order to evaluate such conditions.
Techniques have been developed which enable the function of an implant device to be monitored remotely from outside the body of the patient. These techniques involve including one or more sensors in the device for sensing the condition of the device. The device further includes a small transceiver for processing the output of the sensors and transmitting a signal based on the output. Such signal typically is a radio frequency signal which is received by a receiver from outside the body of the patient. The receiver then processes the signal in order to monitor the function of the device.
Micro-miniature sensors have been proposed for use in implant devices. For example, PCT Application WO 98/29030 to Govari et al. discusses the use of piezoelectric pressure sensors or micro-machined silicon strain gages in a stent. Pressure changes from one sensor to another are considered indicative of constriction of the stent. U.S. Pat. No. 5,807,258 to Cimochowski et al. describes using surface acoustic wave (SAW) sensors in a graft. Transit times or Doppler measurements using the SAW sensors enable one to determine fluid flow or velocity.
In each such case, however, the amount of constriction (i.e., build up of restenosis or other biological matter) can only be inferred and is not directly measured. For example, blood flow or velocity may not be noticeably affected until after the build-up of a significant amount of restenosis. This can lead to false diagnoses and/or require occlusion be in a more advanced state prior to detection. Furthermore, measurements based on transit times or Doppler measurements, for example, can require complex processing which expose such approaches to another source for error.
In view of the aforementioned shortcomings associated with conventional implant devices, there is a strong need in the art for a medical implant device which can detect the buildup of biological matter more directly compared to conventional devices. There is a strong need for a medical implant device which can provide an indication of the amount of occlusion, extent of infection, etc. more directly and which can be remotely interrogated simply and reliably.